The fluorinated fluorosulfonylalkyl vinyl ether represented by the general formula: CF2═CFOCF2CF2SO2F is a compound that is useful as a starting material for the industrial production of ion exchange membranes, etc.
For the production of a sulfonyl vinyl ether such as the fluorinated fluorosulfonylalkyl vinyl ether, British Patent No. 1,034,197 discloses a method of adding hexafluoropropylene oxide to FCOCF2SO2F and then thermally decomposing the obtained sulfonyl fluoride derivative. In this method, when two or more molecules of hexafluoropropylene oxide are added to FCOCF2SO2F, a sulfonyl vinyl ether represented by CF2═CFO(CF2CF(CF3)O)nCF2CF2SO2F can be obtained. However, when one molecule of hexafluoropropylene oxide is added to FCOCF2SO2F, the main product is a cyclization product represented by the following formula: with the result that the fluorinated fluorosulfonylalkyl vinyl ether represented by CF2═CFOCF2CF2SO2F can hardly be obtained.
Japanese Unexamined Patent Publication No. 1982-28025 discloses a method of adding chloropentafluoropropylene oxide to FCOCF2SO2F and thereafter conducting thermal decomposition. This method can provide a fluorinated fluorosulfonylalkyl vinyl ether; however, chloropentafluoropropylene oxide, which is used as a starting material, cannot be obtained in high yield, so that the fluorinated fluorosulfonylalkyl vinyl ether cannot be efficiently produced at low cost.
Other attempts to produce sulfonyl vinyl ethers include a method of converting the halogen of a halogen-terminated vinyl ether to an SO2F group as disclosed in Japanese Unexamined Patent Publication No. 1986-30552; a method of dechlorinating CF2ClCFCOCF2CF2SO2F using zinc, as disclosed in Japanese Unexamined Patent Publication No. 1999-228474; etc.
These methods, however, fail to give a good yield of sulfonyl vinyl ether, which is the intended product. Therefore, they are not satisfactory as industrial production methods.
U.S. Pat. No. 3,560,568 discloses a method of using FCOCF(CF3)OCF2CF2SO2F as a starting material, forming its cyclization product, carrying out ring opening using CH3ONa to form CF2═CFOCF2CF2SO3Na, chlorinating the terminal SO3Na group with PCl5 to synthesize CF2═CFOCF2CF2SO2Cl, and then fluorinating it with NaF to convert the SO2Cl group to an SO2F group. This method, however, is very inefficient since CF2═CFOCF2CF2SO3Na shows extremely low chlorination reactivity. The method also has disadvantages such as the generation of HCl gas when water is present in the reaction system. In addition, the method requires the almost complete removal of impurities such as NaF before the chlorination reaction, and involves the difficulty of separating the by-product POCl3 from the chlorination product CF2═CFOCF2CF2SO2Cl by distillation. The production process is thus very complicated, making the industrial practice of this method very difficult.